The present invention relates to compositions and methods for decreasing hydrogen permeation into metal equipment used in wet refinery environments containing hydrogen sulfide, ammonia, and cyanide.
An area of concern in refinery operations is hydrogen permeation into the equipment of water handling systems used to remove water soluble contaminants in several parts of the refining process. Crude oil containing nitrogen and sulfur compounds gives rise to a variety of water soluble compounds when the crude is catalytically or thermally cracked and fractionated. These compounds include ammonia, hydrogen sulfide, hydrogen cyanide (HCN) and numerous organic species having ionizing cyanide, sulfide (S2xe2x88x92), or ammonium (NH4+) substituents.
Ammonia is known to react with hydrogen sulfide to give ammonium sulfide, which reacts further with hydrogen sulfide to give ammonium bisulfide. The bisulfide ion reacts with iron at the surface of the handling equipment to form ferrous sulfide. At the same time, atomic hydrogen is liberated. The cyanide ion is believed to destabilize the iron sulfide and to retard the recombination of atomic hydrogen into gaseous hydrogen. As a result, the surface concentration of atomic hydrogen increases. Atomic hydrogen is small enough to pass through the crystal lattice of the steel and, because of the concentration driving force, to pass through the steel and into the atmosphere. In the process, the steel becomes saturated with hydrogen and is considered to be hydrogen charged.
Steel in a hydrogen charged condition is subject to several cracking mechanisms, including sulfide stress cracking, hydrogen blistering, and stress-oriented hydrogen-induced cracking. The hydrogen permeating through the steel will run into a flaw, a dislocation, or a hole in the metal. Hydrogen atoms that recombine at this location form hydrogen gas, which tends to become stuck in the steel because the molecules are too large to move through the steel crystal lattice. As more and more hydrogen gas is trapped in the flaw, the pressure inside the metal starts to build. When the pressure at the flaw reaches the yield strength of the metal, the mechanical properties of the metal start to fail.
A number of materials have been used to inhibit hydrogen-induced cracking of metal. Unfortunately, none of these materials has been entirely successful.
The present invention provides a composition and method for decreasing corrosion and permeation of hydrogen into metal equipment used in wet refinery environments containing hydrogen sulfide, ammonia, and cyanide comprising incorporating into a product stream handled by said equipment a composition comprising a polyamine amide of 3-hydrocarbyl thiopropionic acid in an amount sufficient to inhibit said hydrogen permeation.
The inhibitor of the present invention is a polyamine amide of 3-hydrocarbyl thiopropionic acid having the following general formula: 
wherein
n is between about 1-6;
wherein R1 is a hydrocarbyl group comprising at least about 10 carbon atoms selected from the group consisting of straight, branched, and cyclic alkyl groups, alkenyl groups, and akynyl groups, aryl groups, alkaryl groups, and aralkyl groups, and heterocyclic alkyl groups containing oxygen or nitrogen as a ring constituent; and,
wherein R2 is a nitrogen-containing group selected from the group consisting of a cyclic imide group and a hydrocarbyl amide group wherein a nitrogen in said nitrogen-containing group also comprises a nitrogen of said polyamide, and wherein said cyclic imide group further comprises between about 4-6 carbon atoms, and wherein said hydrocarbyl group has between about 1-20 carbon atoms selected from the group consisting of straight, branched, and cyclic alkyl groups, alkenyl groups, and alkynyl groups.
In a most preferred embodiment, R1 comprises a hydrocarbyl group having between about 10-14 carbon atoms, most preferably about 12 carbon atoms, and R2 is a nitrogen-containing group selected from the group consisting of a cyclic imide group and a hydrocarbyl amide group wherein a nitrogen in said nitrogen-containing group also comprises a nitrogen of said polyamide, wherein said cyclic imide group further comprises between about 4-6 carbon atoms, and wherein said hydrocarbyl amide group comprises at least one oxygen double bonded to said hydrocarbyl in addition to the double-bonded oxygen forming said amide group, said hydrocarbyl group having between about 10-14 carbon atoms selected from the group consisting of straight, branched, and cyclic alkyl groups, alkenyl groups, and alkynyl groups.
The manufacture of a most preferred embodiment results in a mixture of two predominant compounds: propanamide, N-[2-[2-[3-(dodecenyl)-2,5-dioxo-1-pyrrolidinyl]ethyl]amino]ethyl]-3-[dodecylthio]-2-methyl (xe2x80x9cPDDPDMxe2x80x9d), which has the following formula: 
and, 15-thia-5,8,11-triazaheptacosanoic acid, 2-(dodecenyl)-13-methyl-4,12-dioxo (xe2x80x9cTTDMDxe2x80x9d), which has the following formula: 
In other preferred permeation inhibitors, R1 comprises a hydrocarbyl group comprising between about 10-14 carbon atoms, and R2 is selected from the group consisting of a polyalkyleneamine, a nitrogen-containing group selected from the group consisting of a cyclic imide group, and a hydrocarbyl amide group, wherein a nitrogen in said nitrogen-containing group also comprises a nitrogen of said polyamine, and a hydrocarbyl group having between about 5-12 carbon atoms selected from the group consisting of straight, branched, and cyclic alkyl groups, alkenyl groups, and alkynyl groups, wherein said hydrocarbyl group comprises at least one substituent selected from the group consisting of a carboxyl group and an amine group.
Specific examples of such other preferred inhibitors include, but are not limited to the following, which are designated both by structure, and by their xe2x80x9cCAS Index Namexe2x80x9d: 
CAS Index Name

CAS Index Name

CAS Index Name
and 
CAS Index Name
and 
CAS Index Name
In order to measure the efficacy of a hydrogen permeation inhibitor, the hydrogen permeation of a given environment must be measured. The hydrogen charging capability of an environment is measured by the rate of proton discharge and the amount of hydrogen absorbed as a result. Electrochemical hydrogen permeation measurements allow the measurement of hydrogen flux through the material.
In the following experiments, the electrochemical test system was a Devanathan type cell in which a steel membrane or xe2x80x9ccouponxe2x80x9d acted as a bi-electrode. On one side of the membrane or xe2x80x9ccouponxe2x80x9d (the cathodic or charging side), a simulated fluid catalytic cracker (xe2x80x9cFCCxe2x80x9d) solution was added in which hydrogen was deposited due to wet H2S corrosion or artificial charging of the coupon. On the other side of the coupon (the anodic or collecting side), the evolved hydrogen quantity was measured. A separate, electrically isolated solution existed on the collection side of the coupon. Separate electrical circuitry made the anodic or collecting side of the coupon, at which hydrogen was evolved, an anode. Here, the hydrogen that entered the coupon on the input side was anodically dissolved out. The anodic current was a measure of the hydrogen permeation through the coupon. Preferred inhibitors reduced the anodic current of a given control with a minimum corrosion rate of about 80-120 mils per year by at least about 50%, preferably by at least about 60-70%, most preferably by about 75%.
In order to inhibit hydrogen permeation, between about 6-24 ppm, preferably about 12 ppm of the inhibitor should be used based on the hydrocarbon in the system. The inhibitors may be used in high pressure areas, such as after compressors and/or before exchangers, in any type of refinery unit that experiences hydrogen permeation damage. The most common applications for the inhibitors of the present invention are fluid catalytic cracking (FCC) units and cokers which are not equipped with a system to permit water washing of high pressure areas. The inhibitors of the present invention normally will be added where a water wash would be found, if present.
The inhibitors of the present invention can be manufactured by charging a thiol bearing a desired R1 to a reactor along with tetrabutylammonium hydroxide, preferably a 40 wt % by solution, as a catalyst. A desired methacrylate, such as methyl- or allyl-methacrylate, preferably methyl methacrylate, then should be charged to the reactor over a period of about 15 minutes. During this time, the reaction mixture may experience a temperature increase of about 53xc2x0 C. (127xc2x0 F.). The contents should be stirred while cooling for about 15 minutes. During this stirring period, the color of the pot contents may change, for example, from beige to pink to green. After verifying that the desired intermediate has been formed, e.g. using IR analysis, a desired polyalkylenepolyamine, such as diethylene triamine, should be added, and the contents of the reactor should be heated until distillate begins to appear in the overhead [136xc2x0 C. (277xc2x0 F.)]. The heating should be continued, and all of the overhead material should be collected over a period of about 1.5 hours. During this time, the temperature of the material may increase from about 136xc2x0 C. (277xc2x0 F.) to about 180xc2x0 C. (356xc2x0 F.). The distillate should be analyzed, e.g. by IR analysis, to verify that the polyalkylenepolyamine has formed the desired amide.
Thereafter, the reactor contents should be cooled to about 80xc2x0 C. (176xc2x0 F.), and a compound that will react with the free NH2 group at the end of the polyalkylenepolyamine to form a desired R2, e.g., dodecenyl succinic anhydride, should be charged to the reactor over a xc2xd hour period with no heating or cooling, resulting in an exotherm. The reactor contents should be heated to ref lux and a steady flow of distillate collected. When no more distillate is coming overhead, the reactor contents should be cooled while mildly blowing nitrogen into the system to prevent air oxidation of the contents at the high temperature.
When the temperature drops to about 70xc2x0 C. (158xc2x0 F.), nitrogen should be discontinued and a sample should be taken for IR analysis to confirm that the desired inhibitor has been formed. The temperature should be maintained above 60xc2x0 C. (140xc2x0 F.) and a desired amount of solvent, such as Fina Solv-150(trademark), should be added and mixed for about 15 minutes. At this point, the product may be transferred to drums or other vessels for use or storage.
Without limiting the present invention, the mechanism of the foregoing reaction is believed to be as follows:
Step 1 
Step 2 
Step 3 
The invention will be better understood with reference to the following examples, which are illustrative only, and should not be construed as limiting the present invention.